Network Working Group T. Clausen
Request for Comments: 5148 LIX, Ecole Polytechnique, France
Category: Informational C. Dearlove
BAE Systems Advanced Technology Centre
B. Adamson
U.S. Naval Research Laboratory
February 2008
Jitter Considerations in Mobile Ad Hoc Networks (MANETs)
Status of This Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Abstract
This document provides recommendations for jittering (randomly
modifying timing) of control traffic transmissions in Mobile Ad hoc
NETwork (MANET) routing protocols to reduce the probability of
transmission collisions.
Table of Contents
1. Introduction ....................................................2
2. Terminology .....................................................3
3. Applicability Statement .........................................4
4. Protocol Overview and Functioning ...............................4
5. Jitter ..........................................................5
5.1. Periodic Message Generation ................................5
5.2. Externally Triggered Message Generation ....................6
5.3. Message Forwarding .........................................7
5.4. Maximum Jitter Determination ...............................8
6. Security Considerations .........................................9
7. References .....................................................10
7.1. Normative References ......................................10
7.2. Informative References ....................................10
Appendix A. Acknowledgements ......................................11
Clausen, et al. Informational [Page 1]RFC 5148 Jitter February 20081. Introduction
In a wireless network, simultaneous packet transmission by nearby
nodes is often undesirable. This is because any resulting collision
between these packets may cause a receiving node to fail to receive
some or all of these packets. This is a physical problem, which
occurs before packets can be inserted into the receiver queue.
Depending on the characteristics of the medium access control and
other lower layer mechanisms, in particular whether retransmission of
unacknowledged packets is supported, this may cause at best increased
delay, and at worst complete packet loss. In some instances, these
problems can be solved in these lower layers, but in other instances,
some help at the network and higher layers is necessary.
This document considers the case when that help is required, and
provides recommendations for using jitter (randomly varying timing)
to provide it. It is possible that the techniques described here
could be implemented either by IP protocols designed for wireless
networks or in conjunction with lower-layer mechanisms.
The problems of simultaneous packet transmissions are amplified if
any of the following features are present in a protocol:
Regularly scheduled messages - If two nodes generate packets
containing regularly scheduled messages of the same type at the
same time, and if, as is typical, they are using the same message
interval, all further transmissions of these messages will thus
also be at the same time. Note that the following mechanisms may
make this a likely occurrence.
Event-triggered messages - If nodes respond to changes in their
circumstances, in particular changes in their neighborhood, with
an immediate message generation and transmission, then two nearby
nodes that respond to the same change will transmit messages
simultaneously.
Schedule reset - When a node sends an event-triggered message of a
type that is usually regularly scheduled, then there is no
apparent reason why it should not restart its corresponding
message schedule. This may result in nodes responding to the same
change also sending future messages simultaneously.
Forwarding - If nodes forward messages they receive from other nodes,
then nearby nodes will commonly receive and forward the same
message. If forwarding is performed immediately, then the
resulting packet transmissions may interfere with each other.
Clausen, et al. Informational [Page 2]RFC 5148 Jitter February 2008